Microwave cooking has become very popular and its use will continue to increase. The concept of microwave cooking is that within an enclosed oven, a magnetron tube generates microwave energy, a form of high frequency radio wave energy, and cooks by exciting the molecules, particularly water, comprising the food. The manufacturers of microwave ovens warn purchasers not to operate the oven without any material in the oven. Operating the oven when it is empty can result in the magnetron tube being damaged by reabsorbing the microwave energy. The damage can occur in a relatively short period of time. Depending on the model of machine, control setting and other factors, the magnetron tube can be permanently damaged in 12 to 15 minutes. The magnetron tube is one of the more expensive components of the microwave oven. It is also possible that the microwave oven could catch fire if the magnetron tube overheated.
The various models of microwave ovens have different operational controls. Generally, the more expensive the model, the more sophisticated the operational controls. The more basic models can be accidentally started without food or other material in the oven. Some models provide for a time period to cook food. If food is removed from the oven prior to the expiration of the time period and the time is not reset to zero, the magnetron tube can be reactivated simply by accidentally pushing the restart button. It is also possible that children can start the cooking cycle by pushing the operational controls in the proper sequence. It is advisable to place a cup of water in the oven at all times that the oven is not being used.
With respect to microwave energy, materials are absorbers, transmitters or reflectors. The molecular structure of foods, particularly the water component, are good absorbers of microwave energy. This is why food cooks so readily. Materials, such as glass, paper, china and some plastics have a molecular structure that allows microwave energy to be transmitted throughout the material without affecting the material or the energy. This characteristic of these materials makes them excellent cooking utensils for microwave ovens. Metals neither absorb nor transmit microwave energy but reflect it. Metals are used in the walls, door and some other components of the microwave oven to reflect the microwave energy for proper heating of the food.